1. Field of the Invention
The present invention relates to a light coupling device and an image projection apparatus using the same and, more particularly, to a light coupling device and an image projection apparatus using the same, which employ optical fibers to project red, green, and blue (R, G, and B) laser beams onto multiple screens, respectively.
2. Description of the Related Art
A projector is an image projection apparatus showing images by projecting inputted image signals onto screens. Such an image projection apparatus is mainly employed to give presentations in conference rooms or to implement projectors in theaters and home theater systems.
Prior art methods for implementing a large screen magnify images through lenses and project images onto screens, wherein the images appear on liquid crystal displays (LCDs) or on cathode ray tubes (CRTs). However, while such methods magnify images, they do not provide clear image quality. In order to solve this problem, an image projection apparatus using digital micromirror device (DMD) panels is presently employed.
The DMD is a semiconductor optical switch using micromirrors. The micromirrors control light reflections based on an inputted image signal. The DMD is of digital fashion so that it has a good color reproductivity and a high contrast ratio with respect to image signals. Further, the DMD does not require A/D and D/A conversions so that it implements clear images.
FIG. 1 shows an exemplary embodiment of a conventional image projection apparatus implementing images on multiple screens.
Referring to FIG. 1, a conventional image projection apparatus 100 has a light source 110, a first high-reflection mirror 115, first and second dichroic mirrors 120 and 130, a second high-reflection mirror 140, first, second, and third condenser lenses 122, 132, and 142, first, second, and third optical fibers 124, 134, and 144, and first, second, and third light scan parts 150, 160, and 170.
FIG. 1 shows solid lines indicating paths for red light beams, which are equally divided into three light beams by the first optical fiber 124 so as to travel to the respective light scan parts 150, 160, and 170. FIG. 1 further shows one-dot chain lines indicating paths for green light beams, which are equally divided into three light beams by the second optical fiber 134 so as to travel to the respective light scan parts 150, 160, and 170, and two-dot chain lines indicating paths for blue light beams, which are equally divided into three light beams by the third optical fiber 144 so as to travel to the respective light scan parts 150, 160, and 170.
The light source 110 emits white light, such as a laser beam. The first high-reflection mirror 115 reflects the light emitted from the light source 110 to change its path. The first and second dichroic mirrors 120 and 130 selectively reflect or transmit the light reflected and incident from the first high-refection mirror 115.
The first dichroic mirror 120 reflects red light beams of the incident light and transmits green and blue light beams. The second dichroic mirror 130 reflects green light beams and transmits blue light beams, which both pass through the first dichroic mirror 120. Finally, the second high-reflection mirror 140 reflects blue light beams.
The first, second, and third condenser lenses 122, 132, and 142 collect red, green, and blue light beams, respectively. Red light beams reflected from the first dichroic mirror 120 are collected into the first optical fiber 124 by the first condenser lens 122. Likewise, green light beams reflected from the second dichroic mirror 130 are collected into the second optical fiber 134 by the second condenser lens 132; and blue light beams reflected from the second high-reflection mirror 140 are collected into the third optical fiber 144 by the third condenser lens 142.
The output terminals of the first, second, and third optical fibers 124, 134, and 144 are each divided into three regions, respectively. Red light beams incident into the first optical fiber 124 is divided into three equal light beams at the output terminals, which are divided into three regions 124a, 124b, and 124c. The three equal red light beams are respectively incident onto the first, second, and third light scan parts 150, 160, and 170.
Green light beams incident into the second optical fiber 134 is divided into three equal light beams at the output terminals, which are divided into three regions 134a, 134b, and 134c. The three equal green light beams are respectively incident onto the first, second, and third light scan parts 150, 160, and 170. Blue light beams incident into the third optical fiber 144 is divided into three equal blue light beams at the output terminals, which are divided into three regions 144a, 144b, and 144c. The three equal light beams are respectively incident onto the first, second, and third light scan parts 150, 160, and 170.
The light scan parts 150, 160, and 170 are optical instruments, such as liquid crystal projectors. The first light scan part 150 uses red, green, and blue light beams, which are respectively incident after being divided into three equal light beams at the first, second, and third optical fibers 124, 134, and 144 to implement or project an image on a screen, i.e., screen_1. The second and third light scan parts 160 and 170 also use red, green, and blue light beams, respectively, to implement or project images on screens, i.e., screen_2 and screen_3.
However, the conventional image projection apparatus as discussed above is so constructed that the output amounts of the light beams outputted from the optical fibers are always the same. This means that the total output amount of the light beams for an image projected on the screens is the same. Therefore, when an image is simultaneously implemented or projected on multiple screens having different sizes, the image implemented or projected on a screen of large size becomes dark and has a severe degree of image flickering compared to images displayed on the other screens. Further, there exists a problem in that an image size should be reduced in order to solve the darkness and flickering problems.